Implantable stimulation devices are devices that generate and deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable medical device system. For example, the disclosed invention can also be used with a Bion™ implantable stimulator, such as is shown in U.S. Patent Publication 2007/0097719, or with other implantable medical devices.
As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible device case 30 formed of titanium for example. The case 30 typically holds the circuitry and battery 26 necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 102 and 104 couple to the IPG 100 using lead connectors 38a and 38b, which are fixed in a header material 36, which can comprise an epoxy for example. In a SCS application, electrode leads 102 and 104 are typically implanted on the right and left side of the dura within the patient's spinal cord. These leads 102 and 104 are then tunneled through the patient's flesh to a distant location, such as the buttocks, wherein the IPG 100 is implanted.
As shown in cross section in FIG. 3, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as a microcontroller, integrated circuits, and capacitors mounted to the PCB 16. Two coils are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from an external controller 12; and a charging coil 18 for charging or recharging the IPG's battery 26 using an external charger 50. The telemetry coil 13 can be mounted within the header 36 of the IPG 100 as shown.
FIG. 2 shows plan views of the external controller 12 and the external charger 50, and FIG. 3 shows these external devices in cross section and in relation to the IPG 100 with which they communicate. The external controller 12, such as a hand-held programmer or a clinician's programmer, is used to send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data such as therapy settings to the IPG 100 to dictate the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status. As shown in FIG. 3, the external controller 12, like the IPG 100, also contains a PCB 70 on which electronic components 72 are placed to control operation of the external controller 12. The external controller 12 is powered by a battery 76, but could also be powered by plugging it into a wall outlet for example. A telemetry coil 73 is also present in the external controller 12, which coil will be discussed further below.
The external controller 12 typically comprises a user interface 74 similar to that used for a portable computer, cell phone, or other hand held electronic device. The user interface 74 typically comprises touchable buttons 80 and a display 82, which allows the patient or clinician to send therapy programs to the IPG 100, and to review any relevant status information reported from the IPG 100.
Wireless data transfer between the IPG 100 and the external controller 12 preferably takes place via inductive coupling. This typically occurs using a well-known Frequency Shift Keying (FSK) protocol, in which logic ‘0’ bits are modulated at a first frequency (e.g., 121 kHz), and logic ‘1’ bits are modulated at a second frequency (e.g., 129 kHz). To implement such communications, both the IPG 100 and the external controller 12 have coils 13 and 73 respectively. Either coil can act as the transmitter or the receiver, thus allowing for two-way communication between the two devices. Referring to FIG. 4, when data is to be sent from the external controller 12 to the IPG 100 (FSK link 170), coil 73 is energized with alternating current (AC), which generates a magnetic field, which in turn induces a voltage in the IPG's telemetry coil 13. The generated magnetic field is FSK modulated (120) in accordance with the data to be transferred. The induced voltage in coil 13 can then be FSK demodulated (125) at the IPG 100 back into the telemetered data signals. Data telemetry in the opposite direction (FSK link 172) from IPG 100 to external controller 12 occurs similarly. This means of communicating by inductive coupling is transcutaneous, meaning it can occur through the patient's tissue 25.
The external charger 50 is used to charge (or recharge) the IPG's battery 26. Specifically, and similarly to the external controller 12, the external charger 50 contains a coil 88 which is energized via charging circuit 122 with a non-modulated AC current to create a magnetic charging field (174). This magnetic field induces a current in the charging coil 18 within the IPG 100, which current is rectified (132) to DC levels, and used to recharge the battery 26, perhaps via a charging and battery protection circuit 134 as shown. The frequency of the magnetic charging field (e.g., 80 kHz) may differ from that used for FSK telemetry (nominally 125 kHz). Again, inductive coupling of power in this manner occurs transcutaneously.
The IPG 100 can also communicate data back (176) to the external charger 50 using Load Shift Keying (LSK) modulation circuitry 126. LSK modulation circuitry 126 receives data to be transmitted back to the external charger 50 from the IPG's microcontroller 150, and then uses that data to modulate the impedance of the charging coil 18. In the illustration shown, impedance is modulated via control of a load transistor 130, with the transistor's on-resistance providing the necessary modulation. This change in impedance is reflected back to coil 88 (LSK link 176) in the external charger 50, which interprets the reflection at LSK demodulation circuitry 123 to recover the transmitted data. This means of transmitting data from the IPG 100 to the external charger 50 is useful to communicate data relevant to charging of the battery 26 in the IPG 100, such as the battery level, whether charging is complete and the external charger can cease, and other pertinent charging variables. However, because LSK works on a principle of reflection, such data can only be communicated from the IPG 100 to the external charger 50 during periods in which the external charger 50 is active and is producing a magnetic charging field (174).
As shown in FIG. 3, the external charger 50 generally comprises at least one printed circuit board 90, electronic components 92 which control operation of the external charger 50, and a battery 96 for providing operational power for the charger 50 and for the production of the magnetic charging field. Like the external controller 12, the external charger 50 has a user interface 94 to allow the patient or clinician to operate the charger 50. The user interface 94 typically comprises an on/off switch 95 which activates the production of the magnetic charging field; an LED 97 to indicate the status of the on/off switch 95; and a speaker 98 for emitting a “beep” at various times. For example, the speaker 98 can beep if the charger 50 detects that its coil 88 is not in good alignment with the charging coil 18 in the IPG 100. Alignment information can be determined and indicated to the external charger 252 by alignment circuitry 103, which is well-known in the art. In a SCS application in which the IPG 100 is implanted in the patient's buttocks, the external charger 50 is generally positioned behind the patient and held against the patient's skin or clothes and in good alignment with the IPG 100 by a belt or an adhesive patch, which allows the patient some mobility while charging.
As one might appreciate from the foregoing description, the user interface 94 of the external charger 50 is generally simpler than the user interface 74 of the external controller 12. Such user interface simplicity is understandable for at least two reasons. First is the relative simplicity of the charging function the external charger 50 provides. Second, a complicated user interface, especially one having visual aspects, may not be warranted because the external charger 50 may not be visible to the patient when it is used. For example, in a SCS application, the external charger 50 would generally be behind the patient to align properly with the IPG 100 implanted in the buttocks as just discussed. The external charger 50 would not be visible in this position, and thus providing the user interface 94 of the external charger 50 with a display or other visual indicator would be of questionable benefit. Additionally, the external charger 50 may be covered by clothing, again reducing the utility of any visual aspect to the user interface.
Although the simplicity of the user interface 94 of the external charger 50 is understandable, the inventor still finds such simplicity regrettable. Even if operation of the external charger 50 is relatively simple, the fact remains that several pieces of information relevant to the charging process might be of interest to the patient, which charging information is impractical or impossible to present by audible means such as through speaker 98.
For example, it may be desired for the user to have some information concerning the alignment between the external charger 50 and the IPG 100; the status of the IPG's battery 26, i.e., to what level it is charged; how much longer charging might take; the status of the external charger's battery 96; or the temperature of either the external charger 50 or the IPG 100. Temperature information can be particularly important to know for safety reasons, and can be provided by a thermocouple 101 in the external charger, and a thermocouple in the IPG (not shown). Inductive charging can heat both the external charger 50 and the IPG 100, and if temperatures are exceeding high, injury or tissue damage can result. Regardless, despite the importance of such charging information, the user interface 94 does not present such information to the user.
One approach in overcoming these shortcomings is disclosed in U.S. Patent Publication 2010/0305663 (“the '663 Publication”), filed Jun. 2, 2009, and incorporated herein by reference in its entirety. As shown in FIG. 5, the '663 Publication provides an RF communication link 210 between the external charger 50 and the external controller 12 so that they can communicate with each other. RF communication link 210 is enabled by an RF transceiver 202 and an RF antenna 202a in the external controller 12, and a corresponding RF transceiver 200 and antenna 200a in the external charger 50. Link 210 preferably comprises a Bluetooth™ compliant link, or other suitable RF communications protocol such as Zigbee™ WiFi, etc.
The external charger 50 and the IPG 100 can generate a variety of charging information such as those parameters just mentioned that can be transmitted to the external controller 12, where it can be reviewed and controlled by the external controller's 12 user interface 74, which as noted is more sophisticated and easier to view. For example, using RF communication link 210, the user can review the relevant charging information from the external charger 50. Relevant charging information from the IPG 100 such as battery 26 status and temperature can be transmitted via LSK link 176 to the external charger 50, and then sent to the external controller 12 via the RF communication link 210, or could be sent directly to the external controller 12 via FSK link 172. FIG. 6 shows the user interface 74 of the external controller 12 displaying such charging information 232 on its display 82. Some processing of the charging information may occur first in the external controller 12 before it is presented in this manner.
While the system of the '663 Publication provides desirable versatility, the inventors recognize a few drawbacks. For example, the system adds additional hardware components to the external charger 50 and the external controller 12 such as transceivers 200 and 202, antennas 200a and 202a, etc. This additional hardware adds cost, in terms of power and expense, and complexity to the system.
Given these shortcomings, the art of implantable medical devices would benefit from an improved means for providing relevant charging information to a patient, and this disclosure presents solutions.